Microsoft said on Friday that security software firm McAfee's criticism of its provision of security information on the new Vista operating system was "inaccurate and inflammatory".
McAfee is one of several software security firms concerned that Microsoft will wait too long to give information they need to protect customers using Microsoft's new Windows 64-bit Vista.
U.S. software giant Microsoft last week promised the European Commission, with which it is embroiled in a long-running legal battle, that it would provide necessary information to security firms.
McAfee's lawyer in Brussels said earlier that Microsoft had failed to live up to "hollow assurances" to carry out the promises.
Microsoft reacted strongly. "It's unfortunate that McAfee's lawyers are making these kinds of inaccurate and inflammatory statements," said Ben Fathi, corporate vice president of Microsoft's security technology unit.
He said Microsoft was being even-handed in developing the needed software, which would happen "in the months ahead".
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Microsoft said on Thursday it could change Vista to deal with the concerns of security software makers only when an update came out. It gave no timetable.
In the past, the Commission has expressed concerns about delays by Microsoft in providing information to other companies because during that time, those firms have lost market share and eventually been sidetracked.
The problems this time apply to the 64-bit Vista, which will eventually supplant the 32-bit version. Vista is due to be shipped to corporate users next month and sold to the public from January.
Security companies accounting for a majority of the market say they need access to the core, or kernel, of 64-bit Windows to protect customers fully.
Software security companies now have access to the kernel in 32-bit Windows, but Microsoft has put up a wall called "PatchGuard" to protect the 64-bit kernel from hackers. Security software firms say that keeps them out, too.
The Gartner group, which issued a report this week assessing problems Microsoft would have in making needed changes to Vista security, said security software would not deliver full functionality for 64-bit Windows under current conditions.
Gartner, a research and consultancy group, recommended that companies tell Microsoft they would not make a commitment to 64-bit Vista until a firm release date was set for the first set of kernel-control software. Gartner said that might be in 2008, and even then there might not be full functionality.
Microsoft declined to endorse the Gartner estimate or make public one of its own.